Can I convert a bitmap to PNG in memory (i.e. without writing to a file) using only the Platform SDK? (i.e. no libpng, etc.).
I also want to be able to define a transparent color (not alpha channel) for this image.
The GdiPlus solution seems to be limited to images of width divisible by 4. Anything else fails during the call to Save(). Does anyone know the reason for this limitation and how/whether I can work around it?
Update
I implemented the GDI+ solution, but as I said, it's limited to images with quad width. I am seeking to solve this width issue without changing the image dimensions, or an alternative non-GDI+ solution that works.
I read and write PNGs using libpng and it seems to deal with everthing I throw at it (I've used it in unit-tests with things like 257x255 images and they cause no trouble). I believe the API is flexible enough to not be tied to file I/O (or at least you can override its default behaviour e.g see png_set_write_fn in section on customization)
In practice I always use it via the much cleaner boost::gil PNG IO extension, but unfortunately that takes char* filenames and if you dig into it the png_writer and file_mgr classes in its implementation it seem pretty tied to FILE* (although if you were on Linux a version using fmemopen and in-memory buffers could probably be cooked up quite easily).